1. Field of the Invention
The present invention related to an optical module with a sleeve mated with a ferrule secured in an optical connector.
2. Related Prior Art
An ordinary optical module with a function to transmit optical signal applicable in the optical communication with a large capacity and a high transmission speed implements a semiconductor laser diode (hereafter denoted as LD) with a large output power as an optical signal source. Such an optical module provides an optical receptacle to be mated with an optical connector to couple the optical signal with the optical fiber. The optical receptacle optically aligns a ferrule secured in the optical connector with the LD.
As the optical communication becomes popular to be applied in the consumer field, the cost reduction of the optical module is inevitably and continuously requested in the field. The Japanese Patent Application published as JP-2007-121920A has disclosed an optical module with a sleeve to align the ferrule, a support and optical members, in which these parts are integrally molded with resin.
FIG. 3A schematically illustrates the optical module disclosed therein. The module 21 installs an LD 22 on the stem 23 and air-tightly seals the LD 22 by a cap 24 and the stem 23. The member 25 to support the optical fiber covers the cap 24. The supporting member 25 includes a sleeve portion 25a to receive and to align the ferrule 26 attached in the tip of the fiber, a skirt portion to cover the cap and to be attached in a tip thereof with the stem 23, and a lens portion 25c. The supporting member 25 is made of resin transparent in wavelengths of light transmitted in the optical fiber or that emitted from the LD 22. The skirt portion 25b is fixed to the stem 23 with an adhesive curable by the ultraviolet rays, which enables to fix the skirt portion against the stem in a short time and enhances the alignment accuracy between the lens 25c and the LD 22.
In a practical use of the optical module receiving in the receptacle thereof the optical connector with the optical fiber, it may be occurred that an external force or pressure be applied in a direction perpendicular to an optical axis of the ferrule. That is, swinging the fiber extending from the connector, the optical coupling efficiency between the optical connector and the receptacle, namely, between the fiber and the LD, fluctuates. This phenomenon is often called as the wiggle tolerance. Another optical module disclosed in a Japanese Patent Application published as JP-2005-338407A enhances the Wiggle tolerance by implementing the sleeve made of zirconia ceramics which is stiff and accurate but costly material. Moreover, the optical module disclosed therein provides a sleeve cover made of composite materials of resin and meal in order to enhance the stiffness of the optical module.
Such an optical module 31 is illustrated in FIG. 3B, where the module 31 comprises a body 34 and an optical receptacle 35. The body 35 holds the packaged LD 32 and the lens 33. The optical receptacle 35 is, for instance, welded to the base 34. The receptacle 35 secures and fixes a portion of the fiber stub 38, which is supported by a metal holder 36 and provides a short-lengthened fiber 37 in a center thereof. The sleeve 38 made of, for instance, zirconia and aluminum receives another portion of the stub 38 not supported by the metal holder 36, and is set within the sleeve case 40 that is comprised of a front portion 40a made of resin and a rear portion 40b made of metal. Thus, the mechanical stiffness of the receptacle 35 may be secured.
The first optical module illustrated in FIG. 3A provides the member integrally built with the skirt portion, the sleeve portion and the lens, which may simplify the process to obtain the module and reduce the production cost thereof. However, the optical communication system implementing the single mode fiber is necessary to align the fiber optically with the LD within an alignment accuracy of 1 to 3 μm. Nevertheless, the dimensional accuracy of the mold resin is as much as 3 to 4 μm. Therefore, it is quite hard to attain the required accuracy in the sleeve portion even when the inner shape of the sleeve portion is circular.
Moreover, the thermal expansion co-efficient of the resin material is considerably different from that of zirconia ceramics often used as the ferrule. Thus, the accurate alignment between the ferrule made of ceramics and the resin made sleeve is further unattainable in wider temperature ranges.
In addition, the Young's modulus of the mold resin is about 3 GPa after the curing, which is two figures smaller than that of the ziroconia ceramics, 245 GPa, and stainless steel, 219 GPa. Accordingly, the deformation of the resin sleeve may occur by a force applied perpendicular to the sleeve axis, which varies the optical coupling efficiency between the ferrule and the sleeve and degrades the wiggle tolerance.